In such cameras, especially in those provided with interchangeable objectives in which the reflex mirror must be disposed behind an iris diaphragm, it is known to provide a preselector which is adjustable to a desired stop position, the diaphragm being normally biased into its wide-open position from which is it briefly displaced into the preselected position just before the tripping of a shutter by a release button or the like. This enables the operator to use full illumination when sighting and focusing upon an object to be photographed.
Such cameras are generally equipped with a windup handle which is manually operated to advance the film, cock the shutter and possibly carry out additional functions such as reactivating the viewfinder after its disablement upon the previous exposure. With the subsequent actuation of the shutter release, by which a control member coupled with the handle is returned to its original position by a restoring spring, the motion of this control member can be utilized to displace the iris diaphragm into its selected stop position and back to its wide-open position in timed relationship with the opening and closure of the shutter. Such an arrangement, which does not use the windup stroke itself for diaphragm control, has been disclosed in German Pat. No. 2,062,230. That system comprises a cam disk executing a full forward rotation during the windup stroke and a full reverse rotation during the return stroke, a coacting cam follower being connected with the setting ring of the diaphragm through a linkage including a yieldable coupling. The linkage further comprises a relatively complicated system of levers and springs designated to facilitate the escapement of the cam follower during the next windup stroke without entrainment of the setting ring.